1. Technical Field
The present disclosure relates to a backlight assembly and, more particularly, to a backlight assembly capable of obtaining uniform white light, while preventing light leakage; and a liquid crystal display device including the same.
2. Background
A flat panel display (FED) is an improved display device for use in compact, lightweight systems including portable computers such as notebook computers, PDAs, and the like, or portable mobile terminals, and the like, as well as monitors of desktop computers; and replaces conventional cathode ray tube (CRT) display devices.
Currently commercialized flat panel display devices include a liquid crystal display (LCD), a plasma display panel (PDP), an organic light emitting display device, and the like. Thereamong, an LCD used in mobile devices, computer monitors, HDTVs, and the like, has gained prominence due to its advantages such as excellent visibility, ease of a reduction in thickness, low power consumption, a low level of heating, and the like.
An LCD includes a liquid crystal panel including two substrates attached with a liquid crystal layer interposed therebetween, and a backlight assembly providing light from a lower side of the liquid crystal panel.
The backlight assembly uses a cold cathode fluorescent lamp (CCFL), an external electrode fluorescent lamp (EEFL), a light emitting diode (LED), and the like. Thereamong, the LED, having the characteristics such as compactness, low power consumption, high reliability, and the like, is widely used as a light source for displays.
Recently, in order to enhance color gamut (or color reproduction range) of LCDs, a blue LED, replacing a general white LED, is used as a light source of a backlight assembly. Also, a separate optical conversion sheet for converting blue light emitted from a blue LED into white light is provided.
FIG. 1 is a view illustrating a related art LCD device, and FIG. 2 is an enlarged view of a portion ‘A’ of FIG. 1.
Referring to FIG. 1, the related art LCD 1 includes a liquid crystal panel 10, a backlight assembly, and receiving containers for receiving the liquid crystal panel 10 and the backlight assembly, for example, a support main 35, and a bottom cover 30.
The liquid crystal panel 10 has a structure in which two substrates 11 and 13 are attached with a predetermined gap therebetween, and a liquid crystal layer (not shown) is interposed between the two substrates 11 and 13. The liquid crystal panel 10 displays an image as optical characteristics of the liquid crystal layer are changed according to an electric field formed between the two substrates 11 and 13. The liquid crystal panel 10 is driven upon receiving a signal by a driving circuit (not shown) connected to one of the two substrates 11 and 13.
The backlight assembly is disposed below the liquid crystal panel 10 and supplies light to the liquid crystal panel 10. The backlight assembly includes light sources 27 and 28, a light guide plate 25, a light conversion sheet 23, an optical sheet 21, and a reflective sheet 26.
The plurality of blue LEDs 27 and a flexible printed circuit board (FPCB) 28 together form and are referred to herein as a light source. The light sources 27 and 28 include a plurality of blue LEDs 27 and a flexible printed circuit board (FPCB) 28 on which the blue LEDs 27 are mounted. The light sources 27 and 28 emit blue light from the blue LEDs 27.
The light guide plate 25 is disposed to be adjacent to the light sources 27 and 28, and emit blue light, which is incident through a light entrance surface from the light sources 27 and 28, upwardly, namely, through a light exit surface.
The reflective sheet 26 is disposed on a rear surface of the light guide plate 25, and reflects light, which travels to a lower side of the light guide plate 25 from the light sources 27 and 28, to an upper side of the light guide plate 25. The term ‘upper side’ is used herein to refer to a side which faces or is proximal to the light emitting side of the LCD. The term ‘upper surface’ is used herein to refer to a surface that faces the light emitting side of the LCD. The term ‘lower surface’ refers to a surface that is opposite to the ‘upper surface’ or faces away from the light emitting side of the LCD.
The light conversion sheet 23 is disposed on an upper surface of the light guide plate 25 and converts blue light emitted from the light guide plate 25 into white light.
The light conversion sheet 23 may include a plurality quantum dots therein, and a wavelength of blue light provided from the light guide plate 25 is selectively converted by the quantum dots to emit red light and green light. The red light and green light wavelength-converted together with blue light provided from the light guide plate 25 are mixed within (or collectively emitting from) the light conversion sheet 23, thus finally emitting white light.
The optical sheet 21 is disposed on the light conversion sheet 23 and diffuses and concentrates white light output from the light conversion sheet 23. The optical sheet 21 includes one or more prism sheets, and light diffused and concentrated by the optical sheet 21 is provided to a rear surface of the liquid crystal panel 10.
The backlight assembly including the foregoing components are accommodated in the bottom cover 30, and fixed by the support main 35. The liquid crystal panel 10 is disposed on the support main 35. Also, a top cover (not shown) is coupled to the bottom cover 30 from an upper side of the liquid crystal panel 10, thus completing the LCD device 1.
As shown in the portion ‘A’ of FIG. 1, in the related art LCD device 1, the light conversion sheet 23 and the FPCB 28 are disposed to be spaced apart from one another by a predetermined gap on an upper surface of the light guide plate 25. Thus, light emitted from the blue LED 27 is leaked outwardly through the exposed upper surface of the light guide plate 25, causing a light leakage phenomenon.
That is, as illustrated in FIG. 2, the blue LED 27 of the light sources 27 and 28 emit light in a plurality of directions, and the emitted light is incident through the light entrance surface of the light guide plate 25 and reflected and refracted to travel within the light guide plate 25. The light which has travelled to the interior of the light guide plate 25 is emitted upwardly through the light exit surface of the light guide plate 25.
Here, when the light emitted from the blue LED 27 is incident to the light entrance surface of the light guide plate 25 at an accurate incident angle (B), the incident light is reflected and refracted within the light guide plate 25 so as to be emitted to the light exit surface where the light guide plate 25 and the light conversion sheet 23 overlap with each other. The light conversion sheet 23 converts light provided from the light guide plate 25, namely, blue light, into white light and provides the white light to the optical sheet 21.
However, if light emitted from the blue LED 27 is incident to the light entrance surface of the light guide plate 25 at an inaccurate incident angle (B′), the incident light is reflected and refracted within the light guide plate 25 so as to be output outwardly through the exposed upper portion of the light guide plate 25.
Thus, in the related art LCD device 1, since the FPCB 28 and the light conversion sheet 23 are disposed to be spaced apart from one another by a gap on the light guide plate 25, light emitted from the blue LED 27 is leaked outwardly through the exposed upper portion of the light guide plate 25, causing light leakage.
The light leakage causes a bluish appearance on one side of the liquid crystal panel, which results in a defective screen image of the LCD device 1.